Multi-stage centrifugal pump with means for pulse cancellation

ABSTRACT

A multi-stage, double volute, centrifugal pump has an intermediate discharge and a final discharge constructed so that the pulses in the fluid at the discharge stages created by the impeller vanes passing the lips of the volute are eliminated within the pump assembly by the use of an impeller having an odd number of vanes and the volute lips are located 180* apart, and separate flow paths of equal length lead from each lip to a zone of confluence. The point of convergence for the intermediate discharge is in the pump case, the point of convergence for the final discharge is also in the pump case.

United States Patent 1191 Shuey et al.

MULTI-STAGE CENTRIFUGAL PUMP WITH MEANS FOR PULSE CANCELLATION Inventors: Scott James Shuey, Fullerton;

Wallace Leland Smith, Santa Ana;

Harold G. Wilk, Los Angeles, all of Calif.

Assignee: Borg-Warner Corporation, Chicago,

Filed: Nov. 6, 1972 Appl. No.: 303,891

us. 01 415/198, 415/104, 415/199 A Int. Cl. FOld 1/02 Field of Search 415/108, 198, 199 A Jan. 29, 1974 2,108,786 2/1938 Bigelowetal. ..4l5/l99A 2,601,828 7/1952 Lobanoff ..4|5/108 2,925,042 2/1960 Lutz ..4|5/108 Primary ExaminerC. J. Husar Attorney, Agent, or FirmDonald W. Banner et a1.

[ 5 7] ABSTRACT A multi-stage, double volute, centrifugal pump has an intermediate discharge and a final discharge constructed so that the pulses in the fluid at the discharge stages created by the impeller vanes passing the lips of the volute are eliminated within the pump assembly by the use of an impeller having an odd number of vanes and the volute lips are located 180 apart, and separate flow paths of equal length lead from each lip to a zone of confluence. The point of convergence for the intermediate discharge is in the pump case, the point of convergence for the final discharge is also in the pump case.

11 Claims, 4 Drawing Figures PAIENTEI] JANZS I974 SHEEI 1 OF 3 PAIENTED JAN 2 9 1974 saw 3 0F 3 MULTI-STAGE CENTRIFUGAL PUMP WITH MEANS FOR PULSE CANCELLATION BACKGROUND OF THE INVENTION In the operation of certrifugal pumps of the type wherein impeller vanes pass the lips of volute passageways at the pump discharge stage, either at an intermediate discharge stage or at the final discharge state, problems have been experienced in the pump assemblies and in the conduits downstream from the discharge outlet due to the pressure pulses of significantly high amplitude caused when such pumps are operating at high speed and at high pressure, such as boiler feed pumps, for example, or other pumps where speed ranges above 4,000 revolutions per minute and pressure ranges above 4,000 p.s.i. The problem also exists in other, lower speed and pressure pumps, but the effects are less pronounced.

More particularly, such pumps may be damaged by the fracturing of diaphragms or dividers between the stages when the downstream conduits are vibrated by the pulses, sometimes resulting in sympathetic vibration of certain lengths of the downstream conduit and increased pressure pulses, that destruction of the conduit or its mountings or equipment in the conduit may result. The problem is peculiar in multi-stage centrifugal pumps to the pump discharge stage, either the final discharge or an intermediate discharge stage, where an intermediate take-off exists, due to the inherent characteristic of such pumps that the preliminary stages in multi-stage pumps involve volute passages leading from diametrically spaced volute lips at one stage to the next pump stage, which volute passages are of equal length, so that the pulses produced at the volute lips by the vanes of impellers having an odd number of equally spaced vanes are effectively eliminated by cancellation as the 180 out-of-phase pluses converge at the eye of the impeller of the next stage where there is a zone of confluence, Typically, however, at the discharge stage, when the discharge is at an intermediate portion of a multi-stage pump, the flow paths of the fluid flowing from the volute lips to the discharge outlet are of normally unequal length, so that the pressure pulses are not cancelled and therefor travel downstream. Likewise, the provision ofa final stage discharge in a multistage centrifugal pump of the type wherein the direction of pump fluid flow is reversed to balance axial forces on the shaft has also involved flow paths of unequal lengths from the final stage volutes to a discharge opening at one side of the pump.

SUMMARY OF THE INVENTION The present invention involves the provision in a multiplestage, double volute centrifugal pump at its discharge stage, either an intermediate discharge stage or a final discharge stage, an arrangement whereby the pressure pulses produced at the volute lips as the impeller passes the volute lips are cancelled. More particularly, the invention provides a discharge stage structure wherein the impeller has an odd number of equally spaced vanes, the volute lips are located at diametrically opposite locations and the flow passages downstream of the volute lips are of corresponding length and converge at a common location or zone of confluence at which the pressure pulses, being l80 out-of-phase, are effectively cancelled within the pump assembly, thereby protecting the downstream conduit and equipment therein, such as valves, instruments and the like, from being subjected to the pressure pulses. With such a construction in the pump the problem of pressure pulses occurring in the downstream conduit where the conduit is ofa resonant length is completely avoided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I-is a view in longitudinal section ofa double volute, split case, multiple stage pump embodying the invention and providing for pulse cancellation at an intermediate discharge and a final discharge;

FIG. 2 is a fragmentary transverse section, as taken on the line 2-2 of FIG. 1;

FIG. 3 is a fragmentary transverse section, as taken on the line 3-3 of FIG. 1; and

FIG. 4 is a fragmentary transverse section, as taken on the line 44 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The illustrative pump is in most respects typical of a boiler feed pump adapted to supply water to the boiler at fairly high pressure, say 4,500 p.s.i. A barrel 10 has a bore 11 adapted to receive a double volute case 12 which is composed of companion half parts secured together at a middle plane by fasteners 14. At the ends of the barrel 10 are covers 15 and 16, secured in place by suitable fastenings l7 and 18, respectively. The pump shaft 19 is typically rotatably supported in bearing assemblies (not shown) and extends through the covers 15 and 16 and suitable bushings 20 and 21 and seals are provided to prevent leakage of pump fluid from the barrel 10.

An inlet 22 and an outlet 23 are provided in the barrel 10, the inlet being adjacent to an end of the barrel and the outelt being located between the ends of the barrel. The present pump has five stages, but other stage arrangements may be employed. The first stage S1 comprises a double suction impeller 24 mounted on the shaft 19 and keyed at 25 for rotation with the shaft, within stage rings 26 which are fixed in the volute case 12. The impeller 24, as is typical, has oppositely opening eyes 27 to which fluid to be pumped is respectively supplied through the suction inlet 22, via a cavity 28, defined between the volute case 12, the barrel l0 and the end closure 16, and via an inlet port or passage 29 in the volute case 12.

As the impeller 24 revolves, fluid is carried by a number of circumferentially spaced vanes 24v to volute passages 30 formed in the respective volute case parts, these passages 30 arching longitudinally of the assembly, as shown in broken lines at 30a, to conduct fluid to the second pump stage S2. In the inlet passage 29 and in the portion 30a of each volute passage 30, are the usual splitters or baffles 31, 32, respectively, which are employed to prevent swirling of the pump fluid, as it enters the first pump stage S1 and as it enters the second pump stage S2, under the influence of the rotating pump elements.

At the second pump stage S2 is a single suction impeller 33 having an eye 34 and vanes 34v for impelling fluid to opposed volute passages 35 having portions 35a leading to the next successive pump stage S3, which, like stage S2, has an impeller 36 with vanes 36v for impelling fluid into opposed third stage outlet passages 37. These passages 37 constitute long cross-over passages having portions 370 leading to the left, as seen in FIG. 1, past the respective fifth and fourth pump stages S and S4 to the eye 38 of the fourth stage impeller 39 having vanes 39v for impelling fluid into the volute passages 40 having arched portions 401: leading to the eye 41 of the fifthstage impeller 42 which, in turn, has vanes 41v for impelling fluid into outlet passages 42.

As thus far described, the multi-stage pump structure is essentially conventional, and the forces on the shaft 19 are essentially balanced by the oppositely working pump stages 51, S2. and stages S3 and S4, and by the double suction impeller at the first pump stage S1.

Ordinarily, the discharge of fluid from the last or discharge pump stage S5 or from any intermediate stage causes pressure pulses in the discharge fluid stream which are or can be damaging to downstream piping or equipment and may be damaging to the pump. As pointed out above, such pulses are caused when the impeller vanes pass the lips of the volutes, the lips being designated 301, 351, 371, 401 and 421 at the respective pump stages S1 through S5. In accordance with the present invention, however, such pulses are cancelled by providing equal length flow paths leading from the lips to a common point of convergence and by utilizing an odd number of equally spaced impeller vanes, with the volute lips located at diametrically spaced locations, whereby as the out-oflphase pulses reach the point of convergence, the pulses are cancelled.

Intermediate discharge from pumps of the type here involved may be desired, for example, to supply cooling water to the steam boiler to control the steam temperature. In other applications, an intermediate discharge may be utilized for any purpose wherein there is a need for taking off pump fluid in advance of the final discharge stage. In the present p ump, an intermediate discharge is provided at the second pump stage S2, as best seen in FIGS. 2 and 3.

As seen in FIG. 3, the volute lips 351 at the entrance to the respective volute passages 35 are located at positions spaced 180, and the impeller 33 has five vanes 34v equally spaced thereabout. Thus, when one vane 34v is passing one lip 351 the vanes at the diametrically opposite side ofthe impeller are at a maximum distance from the other lip 351, whereby the amplitude of the pressure pulses at the two lips is opposite, that is, highest at one lip and lowest at the other lip.

Each volute case section has .a port 50 opening into one of the volute passages 35 at corresponding location 180 apart. and leading to elongated passages 51 in the respective volute case sections. These passages 51 communicate with corresponding conduits 52 which lead to inlets 53 to an annular channel 54, the inlets, as seen in FIG. 2, entering the channel 54 at diametrically spaced locations. The ports 50, passages 51 and conduits 52 provide equal length flow paths leading to the channel 54. The channel 54, as shown. is appropriately provided in the barrel cover 16, and an outlet conduit 0 55 is connected to the channel at a location equally spaced between the inlets 53. Accordingly, it will be seen that the fluid flow paths from the respective volute lips 35] to the outlet 55, at which the flow paths converge. are of corresponding lengths. and when the 180 outof-phase pressure pulses in the fluid stream reach the outlet 54 thepulses are algebraicly cancelled. Thus. the equipment and pipe downstream from the discharge outlet 54 will not be subjected to pressure pulses of the high magnitude produced at the volute lips.

A functionally similar structure is incorporated in the pump for causing pulse cancellation in the final discharge stage SS, as best seen upon reference to FIG. 4. It will be understood that the arrangement of the impel ler 42 at the last pump stage S5 and the volute lips 421 correspond to that shown in FIG. 3, so that out-ofphase pressure pulses will be produced at each lip 421 as the impeller rotates. To enable pulse cancellation a flow structure is incorporared in the volute case 12 which defines with the shaft 19 a common chamber into which fluid flows from-both ofthe fifth stage volute passages 42a. The convergence of fluid in the chamber 60 from the equal length flow paths 42a results in pulse cancellation, as previously described, within the discharge chamber 60. Fluid then flows from the volute case through passages 61 and 62 formed in the case sections, and thence through an annular space 63, which is defined between the case 12 and the barrel 10, to the outlet 23, as shown by the arrows in FIG. 4. Vari ous webs 64 may be provided in the flow passages 61' and 62 to maintain fluid direction, and a barrier 65 may be installed in the annulus 63 to divide the flow. Splitters 66 are also disposed in the chamber 60 to control the direction of flow of pump fluid, as shown by the arrows in FIG. 4.

lt'will now'be understood that attliedischarg'e outlet, both the intermediate outlet and the final outlet, of the illustrative pump, the usual pulses caused by the passage of the impeller vanes past the volute lips are eliminated in the same manner, that is, by utilizing an impeller with an odd number of equally spaced vanes to pump fluid through flow passages of equal length between volute lips spaced and a zone of confluence of the fluid streams or point of convergence within the pump assembly, so that the pressure pulses which are 180 out-of-phase at the point of convergence are cancelled.

We clairnf I 1. ln a centrifugal pump an elongated pump case assembly, a pump shaft rotatable in said case assembly, means rotatably supporting said shaft at the ends of said case assembly, said case assembly having a discharge stage including means defining volute passages and volute lips at diametrically opposite locations, an impeller rotatable with said shaft and having an odd plurality of equally angularly spaced vanes for impelling fluid through said volute passages, means defining within the pump assembly flow paths of equal length having a common point of convergence for causing cancellation at said point of convergence of pressure pulses in the pump fluid caused by passage of said vanes past said volute lips, and means defining a discharge outlet leading from said point of convergence and to a location externally of said case assembly.

7 2. In a centrigu gal pump as defined in claim 1, said case assembly having a plurality of preliminary pump stages and including one of said discharge stages at the final pump stage and at an intermediate pump stage.

3. In a centrifugal pump as defined in claim 1, said case assembly and said shaft defining said common point ofconvergence therebetween, said case assembly having passage means extending radially from said common point of convergence.

4. In a centrifugal pump as defined in claim 1, said flow paths of equal length including a pair of elongated equal length passages spaced at opposite sides of said shaft and each communicating with one of said volute passages, said means supporting said shaft at one end of said case assembly having means defining a passage interconnecting said pair of elongaged passages. and

said discharge outlet opening into said interconnecting passage at a location equi-distant from said elongaged passages.

5. In a centrifugal pump as defined in claim 1, said case assembly having a plurality of preliminary pump stages each having an impeller and volute passages, including a preliminary stage at each of. the opposite sides of said discharge stage, and crossover passage means leading from the volute passages of the preliminary stage at one side of said discharge stage to the preliminary stage at the other side of said discharge stage.

6. In a centrifugal pump asdefined in claim 1, said case assembly having a plurality of preliminary pump stages each having an impeller and volute passages, including a preliminary stage at each of the opposite sides of said discharge stage, and crossover passage means leading from the volute passages of the preliminary stage at one side of said discharge. stage to the preliminary stage at the other side of said discharge stage, said case assembly and said shaft defining said common point of convergence therebetween, said case assembly having passage means extending radially from said common point of convergence.

7. ln a centrifugal pump as defined in claim 1, said case assembly having a plurality of preliminary pump stages each having an impeller and volute passages, including a preliminary stage at each ofthe opposite sides of said discharge stage, and crossover passage means leading from the volute passages of the preliminary stage at one side of said discharge stage to the preliminary stage at the other side of saiddischarge stage, and wherein one ofsaid preliminary stages also includes means defining volute passagesand volute lips at diametrically opposite locations, an impeller rotatable with said shaft and having an odd plurality of equally angularly spaced vanes for impelling fluid through said volute passages, means defining within the pump assembly flow paths of equal length having a common point of convergence for causing cancellation at said point of convergence of pressure pulses in the pump fluid caused by passage of said vanes past said volute lips, and means defining a discharge outlet laterally spaced from said shaft.

8. In a centrifugal pump asdefined in claim 1, said case assembly having a plurality of preliminary pump stages each having an impeller and volute passages, including a preliminary stage at each ofthe opposite sides of said discharge stage, and corssover passage means leading from the volute passages of the preliminary stage at one side of said discharge stage to the preliminary stage at the other side of said discharge stage, and wherein one of said preliminary stages also includes means defining volute passages and volute lips at diametrically opposite locations, an impeller rotatable with said shaft and having an odd plurality of equally angularly spaced vanes for impelling fluid through said volute passages, means defining within the pump assembly flow paths of equal length having a common point of convergence for causing cancellation at said point of convergence of pressure pulses in the pump fluid caused by passage of said vanes past said volute lips, and means defining a discharge outlet laterally spaced from said shaft, said last mentioned flow paths of equal length including a pair of elongated equal length passages spaced at opposite sides of said shaft and each communicating with one of said volute passages of said intermediate stage, said means supporting said shaft at one end of said case assembly having means defining a passage interconnecting said pair of elongated passages, and said discharge outlet opening into said interconnecting passage at a location equidistant from said elongated passages.

9. A multi-stage centrifugal pump comprising: a tubular pump barrel having a bore, a lateral inlet and a lateral outlet, a volute case in said bore, covers at opposite ends of said barrel, a pump shaft rotatably extending through said barrel and said covers, said shaft having a plurality of axially spaced impellers thereon having a central eye and an odd plurality of vanes, said volute case having at each impeller a pair of diametrically spaced volute passages defined by inlet lips and leading to the eye of an adjacent impeller, said volute passages being of equal length, and means defining discharge passage means communicating with said volute passages at one of said impellers and including discharge passages of equal length converging at a common point.

10. A multi-stage centrifugal pump as defined in claim 9, wherein said means defining discharge passage means are located at the final stage of said pump.

11. A multi-stage centrigugal pump as defined in claim 9, wherein said means defining discharge passage means are located at the final stage of said pump and at an intermediate stage of said pump. 

1. In a centrifugal pump an elongated pump case assembly, a pump shaft rotatable in said case assembly, means rotatably supporting said shaft at the ends of said case assembly, said case assembly having a discharge stage including means defining volute passages and volute lips at diametrically opposite locations, an impeller rotatable with said shaft and having an odd plurality of equally angularly spaced vanes for impelling fluid through said volute passages, means defining within the pump assembly flow paths of equal length having a common point of convergence for causing cancellation at said point of convergence of pressure pulses in the pump fluid caused by passage of said vanes past said volute lips, and means defining a discharge outlet leading from said point of convergence and to a location externally of said case assembly.
 2. In a centrigugal pump as defined in claim 1, said case assembly having a plurality of preliminary pump stages and including one of said discharge stages at the final pump stage and at an intermediate pump stage.
 3. In a centrifugal pump as defined in claim 1, said case assembly and said shaft defining said common point of convergence therebetween, said case assembly having passage means extending radially from said common point of convergence.
 4. In a centrifugal pump as defined in claim 1, said flow paths of equal length including a pair of elongated equal length passages spaced at opposite sides of said shaft and each communicating with one of said volute passages, said means supporting said shaft at one end of said case assembly having means defining a passage interconnecting said pair of elongaged passages, and said discharge outlet opening into said interconnecting passage at a location equi-distant from said elongaged passages.
 5. In a centrifugal pump as defined in claim 1, said case assembly having a plurality of preliminary pump stages each having an impeller and volute passages, including a preliminary stage at each of the opposite sides of said discharge stage, and crossover passage means leading from the volute passages of the preliminary stage at one side of said discharge stage to the preliminary stage at the other side of said discharge stage.
 6. In a centrifugal pump as defined in claim 1, said case assembly having a plurality of preliminary pump stages each having an impeller and volute passages, including a preliminary stage at each of the opposite sides of said discharge stage, and crossover passage means leading from the volute pAssages of the preliminary stage at one side of said discharge stage to the preliminary stage at the other side of said discharge stage, said case assembly and said shaft defining said common point of convergence therebetween, said case assembly having passage means extending radially from said common point of convergence.
 7. In a centrifugal pump as defined in claim 1, said case assembly having a plurality of preliminary pump stages each having an impeller and volute passages, including a preliminary stage at each of the opposite sides of said discharge stage, and crossover passage means leading from the volute passages of the preliminary stage at one side of said discharge stage to the preliminary stage at the other side of said discharge stage, and wherein one of said preliminary stages also includes means defining volute passages and volute lips at diametrically opposite locations, an impeller rotatable with said shaft and having an odd plurality of equally angularly spaced vanes for impelling fluid through said volute passages, means defining within the pump assembly flow paths of equal length having a common point of convergence for causing cancellation at said point of convergence of pressure pulses in the pump fluid caused by passage of said vanes past said volute lips, and means defining a discharge outlet laterally spaced from said shaft.
 8. In a centrifugal pump as defined in claim 1, said case assembly having a plurality of preliminary pump stages each having an impeller and volute passages, including a preliminary stage at each of the opposite sides of said discharge stage, and corssover passage means leading from the volute passages of the preliminary stage at one side of said discharge stage to the preliminary stage at the other side of said discharge stage, and wherein one of said preliminary stages also includes means defining volute passages and volute lips at diametrically opposite locations, an impeller rotatable with said shaft and having an odd plurality of equally angularly spaced vanes for impelling fluid through said volute passages, means defining within the pump assembly flow paths of equal length having a common point of convergence for causing cancellation at said point of convergence of pressure pulses in the pump fluid caused by passage of said vanes past said volute lips, and means defining a discharge outlet laterally spaced from said shaft, said last mentioned flow paths of equal length including a pair of elongated equal length passages spaced at opposite sides of said shaft and each communicating with one of said volute passages of said intermediate stage, said means supporting said shaft at one end of said case assembly having means defining a passage interconnecting said pair of elongated passages, and said discharge outlet opening into said interconnecting passage at a location equi-distant from said elongated passages.
 9. A multi-stage centrifugal pump comprising: a tubular pump barrel having a bore, a lateral inlet and a lateral outlet, a volute case in said bore, covers at opposite ends of said barrel, a pump shaft rotatably extending through said barrel and said covers, said shaft having a plurality of axially spaced impellers thereon having a central eye and an odd plurality of vanes, said volute case having at each impeller a pair of diametrically spaced volute passages defined by inlet lips and leading to the eye of an adjacent impeller, said volute passages being of equal length, and means defining discharge passage means communicating with said volute passages at one of said impellers and including discharge passages of equal length converging at a common point.
 10. A multi-stage centrifugal pump as defined in claim 9, wherein said means defining discharge passage means are located at the final stage of said pump.
 11. A multi-stage centrigugal pump as defined in claim 9, wherein said means defining discharge passage means are located at the final stage of said pump and at an intermediate stage of said pump. 